RESEARCH ARTICLE Copyright © 2013 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 13, 1–9, 2013 Metal Doped Nanosized Titania Used for the Photocatalytic Degradation of Rhodamine B Dye Under Visible-Light Mphilisi M. Mahlambi 1 , Ajay K. Mishra 1 , Shivani B. Mishra 1 , Rui W. Krause 1 , Bhekie B. Mamba 1 ∗ , and Ashok M. Raichur 1 2 1 Department of Applied Chemistry, University of Johannesburg, P.O. Box 17011, Doornfontein 2028, South Africa 2 Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India Metal-doped anatase nanosized titania photocatalysts were successfully synthesized using a sol–gel process. Different amounts of the dopants (0.2, 0.4, 0.6, 0.8 and 1.0%) of the metals (Ag, Ni, Co and Pd) were utilized. The UV-Vis spectra (solid state diffuse reflectance spectra) of the doped nanoparticles exhibited a red shift in the absorption edge as a result of metal doping. The metal- doped nanoparticles were investigated for their photocatalytic activity under visible-light irradiation using Rhodamine B (Rh B) as a control pollutant. The results obtained indicate that the metal- doped titania had the highest activity at 0.4% metal loading. The kinetic models revealed that the photodegradation of Rh B followed a pseudo first order reaction. From ion chromatography (IC) analysis the degradation by-products Rhodamine B fragments were found to be acetate, chloride, nitrite, carbonate and nitrate ions. Keywords: Metal Doped Titania, Band Gap, Photocatalytic Degradation, Rhodamine B, Visible-Light Irradiation. 1. INTRODUCTION Photocatalytic degradation of organic pollutants by semi- conductors is of great significance in environmental pol- lution remediation. 1 Among the semi-conductor materials, TiO 2 or titania has been shown to be an excellent catalyst for the degradation of organic pollutants. 2 3 Photocataly- sis by titania is due to the interaction of holes (h +  and electrons (e -  generated by a photon which participates in reductive and oxidative reactions leading to mineralisation of organic compounds to H 2 O and CO 2 . 4 However, the titania anatase phase (photocatalytically active) can only be activated under UV light (387 nm) due to its large band gap of 3.2 eV. 5 Hence shifting the optical response of TiO 2 towards visible-light can enhance its photocatalytical reac- tions towards visible-light. 6 Metal ion doping shifts the absorption edge of tita- nia towards the visible region by creating energy states within the band gap, resulting in its ‘decrease.’ 7 8 This pro- cess improves the defects sites within and on the titania ∗ Author to whom correspondence should be addressed. nanocrystal thus improving the photocatalytic activity. 9 They are nanoscale metal-semiconductor contacts that act as electron scavengers hence resulting in increased photocatalysis. 10 The presence of optimal amount of metal dopants ensures that the metal particles only act as electron traps hence aiding electron–hole separation. 11 In this work we report on the synthesis of transition metal (Ag, Co and Ni) ion-doped titania as well as Pd metal ion-doped titania. The efficiencies of these metal ion-doped titania nanoparticles was determined for the degradation of Rhodamine B under visible-light irradi- ation. Rhodamine B (Rh B) is one of the major pol- lutants obtained from textile and photographic industry effluents. 12 It is part of the xanthene group dyes and has achieved its prominent use due to its good stability as a laser material hence its photodegradation is crucial with regards to textile effluents. Furthermore, it is estimated that about 1–20% of the total world production of dyes is lost to the environment during synthesis and dyeing processes. These textile effluents are an environmental burden as they contain a large amount of azoic, anthraquinonic and heteropolyaromatic dyes. 13 The discharge of these highly J. Nanosci. Nanotechnol. 2013, Vol. 13, No. xx 1533-4880/2013/13/001/009 doi:10.1166/jnn.2013.7587 1